I created the bug report: [URL][PS-6756] MY-012985 A long semaphore wait - Percona JIRA
I noticed this in the log:
2019-12-19T08:12:25.030516Z 0 [System] [MY-010910] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.16-7) Percona Server (GPL), Release 7, Revision 613e312.
2019-12-19T08:12:27.503856Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.18-9) starting as process 175120
2019-12-19T08:12:38.587506Z 1 [System] [MY-011090] [Server] Data dictionary upgrading from version '80016' to '80017'.
2019-12-19T08:12:39.402430Z 1 [System] [MY-013413] [Server] Data dictionary upgrade from version '80016' to '80017' completed.
2019-12-19T08:12:44.208245Z 4 [System] [MY-013381] [Server] Server upgrade from '80016' to '80018' started.
2019-12-19T08:12:49.309843Z 4 [System] [MY-013381] [Server] Server upgrade from '80016' to '80018' completed.
The data dictionary upgraded from 80016 to 80017, and not to 80018. Is this normal?